As described in commonly owned U.S. patent application Ser. No. 08/966,502 an automatic lubricant dispenser has a lower housing part formed with an outlet, a piston displaceable along an axis in the lower part and forming therein a compartment, a spindle extending along the axis, threaded into the piston, having an upper end above the piston provided with a lower coupling half, and a body of fluent lubricant filling the compartment and forming with the spindle, piston, and lower housing part a lower subassembly. An upper housing part securable to the lower part via a screwthread forms an upper subassembly. An insert mainly in the upper housing part forms a battery compartment and carries a motor unit having an output shaft projecting downward therefrom at the axis and provided with an upper coupling half axially engageable with the lower coupling half. The coupling halves are axially engageable to rotationally couple the motor output shaft to the spindle. A battery is provided in the battery compartment and a circuit board fixed to the insert is connected between the battery and the motor unit. An on-off switch mounted on the circuit board is actuatable to energize the motor unit from the battery. The insert, motor unit, battery, circuit board, and switch together forming a core subassembly normally held between the upper and lower subassemblies.
Thus with this system when the dispenser is empty the upper part of the housing forming the upper subassembly can be removed and then the core subassembly lifted out with the motor, control circuit, and batteries. This leaves the lower subassembly formed by the plastic lower housing part, plastic piston, and normally metallic spindle which are disconnected, discarded, and replaced with a full core assembly comprising a new lower housing part, lubricant body, piston, and spindle. When the insert is reinstalled the connection is made between the motor output shaft and spindle so resetting the upper housing part permanently puts the assembly back together. Since the lower subassembly forms a disposable refill, the piston will be perfectly positioned so that when the device is restarted lubricant will be emitted with the first cycle. In addition it is possible to standardize the dimensions of the core and upper subassemblies, providing longer or shorter lower subassemblies depending on how much lubricant is needed.
With such a system once the machine is turned on the controller periodically energizes the motor. A motion detector associated with the motor output shaft delivers normally one pulse per revolution of this shaft to the controller which deenergizes the motor after a predetermined number of revolutions which corresponds to expulsion of a predetermined dose of lubricant from the outlet. Thus periodically the motor is started and then, after a predetermined dose is expelled from the outlet, the motor is stopped. Actual displacement of the piston is monitored rather than simple motor-energization time since the viscosity of the lubricant will change with temperature and the back pressure can vary, making the amount of lubricant pumped out independent of the actual pumping time.
This type of dispenser is effective for machines which operate continuously. If, however, a thorough lubrication is not possible for some time there is the danger of misdosing since the signal to initiate lubrication will not come often enough. Thus when the machine being lubricated is not in continuous service, the lubrication offered by such dispensers is ineffective. More particularly if the machine is shut down just before it is due for an automatic lubrication cycle, when it is started up again the timer built into it goes through its entire cycle before lubricating again, so that in effect the time between succeeding lubrications will be excessive.